Characterization and quantification of biochar alkalinity

Can the aging process necessarily weaken the effect of biochar on cadmium-contaminated soil remediation: considering biochar at different pyrolysis temperatures and aging treatment

Biochar has widely used to immobilize soil heavy metals in recent years, while the properties of biochar varied with environmental conditions. The influence of biochar aging on fixation and speciation transformation of Cd in soil remains unclear. This study explores how biochar aging affects the fixation and speciation transformation of Cd in soil. Rice straw biochar (RBC) prepared at different pyrolysis temperatures (300 °C, 500 °C, and 700 °C) was aged under three treatments (drying and watering cycle (DW), H2O2 oxidation (HO), and citric acid acidification (CA)) to investigate the effects of the aging process on the adsorption and passivation capacity for Cd. Results showed that the aging treatment increased Cd adsorption on RBC300 by 73.69% to 216.15%, while adsorption on RBC500 and RBC700 decreased by 11.52% to 74.56% and 7.40% to 75.89%, respectively. The addition of both fresh and aged RBC raised pH, DOC, and TOC in Cd-contaminated soil, aiding in Cd fixation. Either fresh or aged RBC addition enhance the stability of Cd in soil. Compared to CK treatment, residual Cd content rose by 28.63% to 43.71%, while both acid-extractable and reducible Cd contents decreased by 9.144% to 10.95%. Furthermore, the available Cd content in the soil saw a reduction of 10.45% to 30.77%, and high-temperature pyrolytic RBC exhibited a stronger capacity for Cd passivation in the soil. Both fresh and aged RBC indirectly reduced Cd bioavailability by affecting soil pH, DOC, and TOC, and the nature aging process (DW) did not weaken the effect of biochar on Cd-contaminated soil remediation. Thus, biochar has a long-term potential for mitigating Cd pollution in farmland.

Synergistic effects of allantoin and Achyranthes japonica-biochar profoundly alleviate lead toxicity during barley growth

Lead (Pb), a toxic metal, causes severe health hazards to both humans and plants due to environmental pollution. Biochar addition has been efficiently utilized to enhance growth of plants as well as yield in the presence of Pb-induced stress. The present research introduces a novel use of biochar obtained from the weed Achyranthes japonica to enhance the growth of plants in Pb-contaminated soil. An experiment was performed with 7 treatments: Control, Pb2+ (10 mg kg-1) only, biochar (4 %) only, allantoin (4 g kg-1) only, biochar combined with Pb2+, allantoin combined with biochar, as well as a combination of allantoin and biochar with Pb2+. Lead toxicity alone markedly diminished plant growth metrics, including root and shoot length, biomass (wet and dry), chlorophyll concentration, and grain production. The application of biochar, allantoin, or their joint administration markedly enhanced the length of shoots (by 50.3 %, 29 %, and 70 %), length of roots (by 69 %, 50 %, and 69 %), and fresh biomass of shoots (by 5 %, 29 %, and 5 %), respectively. This enhancement is ascribed to improved soil characteristics and more efficient absorption of nutrients. The application of biochar, allantoin and their combination improved the tolerance against Pb2+ by increasing the total chlorophyll level by 12 %, 16 %, and 17 %, respectively, vs. the control. Likewise, these amendments significantly (p < 0.05) improved the activity of antioxidant enzymes, including SOD, POD, and CAT by 49 %, 29 %, and 49 %, respectively. The resistance towards Pb2+ was enhanced by biochar, allantoin, and their combined application, with lower Pb2+ concentrations in shoots (59.9 %, 40.1 %, and 49.8 %), roots (48.2 %, 24.1 %, and 58.3 %), and grains (60.2 %, 29.7 %, and 40.1 %) compared to solely Pb-stress, respectively. In summary, converting the weed Achyranthes japonica into biochar and integrating it with allantoin provides an eco-friendly approach to control its proliferation while efficiently alleviating Pb-induced toxicity in plants.

Simultaneous removal of ammonium, phosphate, and phenol via self-assembled biochar composites CBCZrOFe3O4 and its utilization as soil acidity amelioration

ABSTRACTHigh concentrations of ammonium, phosphate, and phenol are recognized as water pollutants that contribute to the degradation of soil acidity. In contrast, small quantities of these nutrients are essential for soil nutrient cycling and plant growth. Here, we reported composite materials comprising biochar, chitosan, ZrO, and Fe3O4, which were employed to mitigate ammonium, phosphate, and phenol contamination in water and to lessen soil acidity. Batch adsorption experiments were conducted to assess the efficacy of the adsorbents. Initially, comparative studies on the simultaneous removal of NH4, PO4, and phenol using CB (biochar), CBC (biochar + chitosan), CBCZrO (biochar + chitosan + ZrO), and CBCZrOFe3O4 (biochar + chitosan + ZrO + Fe3O4) were conducted. The results discovered that CBCZrOFe3O4 exhibited the highest removal percentage among the adsorbents (P < 0.05). Adsorption data for CBCZrOFe3O4 were well fitted to the second-order kinetic and Freundlich isotherm models, with maximum adsorption capacities of 112.65 mg/g for NH4, 94.68 mg/g for PO4 and 112.63 mg/g for phenol. Subsequently, the effect of CBCZrOFe3O4-loaded NH4, PO4, and phenol (CBCZrOFe3O4-APP) on soil acidity was studied over a 60-day incubation period. The findings showed no significant changes (P < 0.05) in soil exchangeable acidity, H+, Mg, K, and Na. However, there was a substantial increase in the soil pH, EC, available P, CEC, N-NH4, and N-NO3. A significant reduction was also observed in the available soil exchangeable Al and Fe (P < 0.05). This technique demonstrated multi-functionality in remediating water pollutants and enhancing soil acidity.

Influence of in situ biochar capping on microbial dynamics and ammonia nitrogen release in sediment

To study the influence of in situ biochar (BC) capping technique on the release of ammonia nitrogen (NH4+-N) from sediments, a field mesocosm experiment was conducted in Baiyangdian Lake (BYDL), a critical water body often referred to as the "kidney of North China" where sediment pollution poses a significant threat to water quality. This study also assessed the impact of BC on sediment microorganisms. The results showed that the NH4+-N concentration in the overlying water of the BC-treated mesocosms was the lowest among four treatments, decreasing to 0.051 mg L-1 by the 60th day. More importantly, the BC treatment showed the least increase in NH4+-N concentrations in sediments compared to other treatments. For sediments capped with a 4 cm layer of BC, the potential release flux of NH4+-N was reduced from 1.84 mg m-2 d-1 to -0.76 mg m-2 d-1. This reduction is likely due to the negatively charged surfaces of biochar, which enhance NH4+-N adsorption through electrostatic interactions. Additionally, BC modified the physical and chemical properties of the surface sediment, improving pH and increasing both organic content and the carbon/nitrogen (C/N) ratio. These changes influenced the microbial community structure within the sediments, enhancing NH4+-N removal. After 60 days, a significant alteration in the microbial community was observed in the BC-treated surface sediments. The addition of BC significantly increased the abundance of Proteobacteria and Firmicutes of the phyla in the sediments. Furthermore, BC enhanced the expression of functional genes including amoA, amoB, nirK, nirS, hzsB, nrfA and ureC, which are likely the primary microbial mechanisms promoting NH4+-N conversion in sediments for final removal.

Influence of biochar derived from Cd polluted silkworm excrement on the phytoavailability of Cd in a paddy soil and its accumulation in mulberry

Developing sericulture industry is a promising model for the utilization of soils heavily contaminated with cadmium (Cd), but the management of polluted silkworm excrement (SE) becomes challenging. This study aimed to evaluate the effects of the SE biochar (SB) with Cd (SB-Cd) and without Cd (SB-Cd free) on the chemical properties of paddy soil, the mulberry leaf quality and the accumulation of Cd in mulberry. The soil incubation experiments showed that the two SBs all raised the acidic soil pH (20.24 %∼49.97 %) significantly (P < 0.05) with the increasing SB addition rates. The two SBs increased the soil cation exchange capacity (CEC) and played an essential role in reducing the phytoavailability of Cd. The pot experiment elucidated the two SBs all promoted the growth of mulberry, increased the crude protein content and the chlorophyll content, reduced the total sugar content in leaves. The Cd concentrations in root, stem, leaf were decreased with the increase of SB respectively, but no significant differences were found between the same additions of SB-Cd free and SB-Cd. The use of SB-Cd for remediation of the Cd polluted soils could be a reasonable method to address the Cd polluted SE.

Improving rice quality through biochar application in China: A meta-analysis

PURPOSE

This research investigates the effects of biochar application on rice quality through a comprehensive meta-analysis, aiming to elucidate the ambiguous impacts of biochar on rice quality indicators and providing a comprehensive quantitative evaluation to inform sustainable agricultural practices and the practical application of biochar in rice cultivation.

DESIGN/METHODOLOGY/APPROACH

Utilizing a systematic meta-analysis, this study extracts 934 pairs of observations from 28 different studies. It integrates data to assess the overarching impact of biochar on rice quality, with a specific focus on ten essential quality indicators: brown rice rate, milled rice rate, head rice rate, chalky rice rate, degree of chalkiness, length-width ratio, amylose content, protein content, gel consistency, and eating quality score. This approach enables a detailed evaluation of how biochar application influences these critical aspects of rice quality.

FINDINGS

The meta-analysis reveals that biochar application notably enhances the processing, appearance, and eating quality score of rice, evidenced by improvements in the brown rice rate by 0.5%, milled rice rate by 1.7%, head rice rate by 6.2%, length-width ratio by 1.4%, and eating quality score by 2.6%. It also substantially reduces the chalky rice rate by 11.1% and the degree of chalkiness by 12.9%. However, the impacts on nutritional indicators, such as amylose content, gel consistency, and protein content, were found to be statistically insignificant. The most favorable effects were observed in heavy loam soil, alkaline soil(pH ≥ 7.5), soil organic content (SOM)＜10 g kg-1, biochar with a pH range of 7-8, high-temperature biochar (≥ 400 °C), and biochar derived from husk and shell.

PRACTICAL IMPLICATIONS

This study highlights biochar's potential to improve rice quality, particularly in terms of processing and appearance, without negatively affecting its nutritional profiles. These findings support the utilization of biochar in rice production to improve quality and provide valuable insights for the development of sustainable agricultural practices and effective biochar application guidelines.

ORIGINALITY/VALUE

This study represents a pioneering effort in agricultural science by systematically quantifying the impact of biochar on key rice quality indicators. It sheds light on the positive effects of biochar in enhancing various aspects of rice quality, underscoring its vital role in promoting sustainable agricultural practices. Through this meta-analysis, the study establishes a foundation for effective biochar usage guidelines in rice cultivation, offering substantial insights and paving new avenues for research into biochar's application in agriculture.

Sugarcane bagasse biochar enhances the growth parameters, haematological parameters, and enzyme activities of genetically improved farmed tilapia (GIFT) reared in inland saline water

In the present scenario, waste management, especially agro-waste, is one of the major challenges. India is an agrarian country and the economy depends on agriculture and a huge amount of agro-wastes are generated. In this study, biochar was prepared from paddy straw and sugarcane bagasse and was used in the feed of genetically improved farm tilapia (GIFT) at 0.5% (w/w) basis to study its effect on growth and haematological parameters. An experiment was carried out in triplicate in 500-l capacity FRP tanks comprising two treatments and one control. Tanks were filled with inland saline soil to maintain 25-cm soil's bed and water with 12 ppt salinity. A total of 22 fish having an average length of 5.14 ± 0.07 cm and weight of 4.8 ± 0.05 g were stocked in each tank; the fish were fed at apparent satiation level, twice daily for 45 days. It was observed that growth parameters like SGR% (specific growth rate), weight gain (WG%), and feed conversion ratio (FCR) were significantly improved (p < 0.05) than the control. Biochar-enriched feed also significantly improved the haematological parameters like red blood cell (RBC), white blood cell (WBC), haemoglobin (Hb) haematocrit % (HCT), mean cell haemoglobin concentration (MCH), and MCV (mean cell volume) in treatment groups than the control. Feeding biochar as feed additives was also found to decrease catalase (CAT) and enhanced amylase and lipase activities in treatments as compared to control (p < 0.05). It can be concluded that the application of biochar as a feed additive enhanced the growth and overall health of the fish, and it can enhance fish production. However, biochar from sugarcane bagasse was found to be more effective than the paddy straw biochar in the diet of tilapia (GIFT).

Application of straw-derived biochar: a sustainable approach to improve soil quality and crop yield and reduce N2O emissions in paddy soil

The burning of agricultural straw is a pressing environmental issue, and identifying effective strategies for the rational utilization of straw resources is decisive for achieving sustainable development. Owing to its high carbon content and exceptional stability, straw biochar produced via pyrolysis has emerged as a key focus in multidisciplinary research. However, the efficacy of biochar in mitigating nitrous oxide (N2O) emissions from paddy soils is not consistent. A 2-year field experiment was conducted and investigated the impact of biochar derived from two feedstocks (rice straw and wheat straw, pyrolyzed at 450 °C) on N2O emissions, global warming potential (GWP), greenhouse gas intensity (GHGI), nitrogen use efficiency (NUE), crop yield, and soil quality. The static chamber technique was used for collecting N2O gas samples, and concentrations were analyzed through gas chromatography methods. The treatment combinations included BR0 (control), BR1 (NPK at the recommended dose, 120:60:40 kg ha-1), BR2 (wheat straw biochar, 5 t ha-1), and BR3 (rice straw biochar, 5 t ha-1). The results exhibited that cumulative N2O emissions from BR2 and BR3 treatments decreased by 10.55% and 13.75% respectively, compared to BR1. Lower GWP and GHGI were observed under both biochar treatments compared with BR1. The highest rice grain yield (3.48 Mg ha-1) and NUE (76.72%) were recorded from BR3, which also exhibited the lowest yield-scaled N2O emission. We observed positive correlations between soil nitrate, ammonia and water-filled pore spaces, while NUE showed negative correlations with N2O emissions. Significant (p < 0.05) improvements in soil quality were also detected in both the biochar treated plots, indicated by increased soil pH, water holding capacity, porosity, and nutrient contents. Overall, the results suggest that applying biochar at a rate of 5 t ha-1 in paddy soil is a viable nutrient management strategy with the potential to reduce reliance on inorganic fertilizers, mitigate N2O emissions, and contribute to sustainable food production.

Pyrolysis of municipal solid waste compost: Pilot plant evaluation as a sustainable practise of waste management

To evaluate the potential of compost based on municipal solid waste (MSW) and 20% legume pruning under a pyrolysis process, generated products, including solids (biochar), liquids (bio-oil), and gases (non-condensable gases), through experimentation in a pilot plant with a fluidized bed reactor at 450°C and gas chromatography/mass spectrometry have been analysed. In addition, the compost kinetic behaviour by thermogravimetric analysis (TGA), using the Flynn-Wall-Ozawa (FWO) method, has been investigated. Four different reaction zones, associated with lignocellulosic materials (hemicellulose, cellulose, and lignin) with a first step for water evaporation, in TGA curve have been observed. A biochar with low stability and aromaticity, considering high and low O/C and H/C ratios, respectively, has been obtained. The obtained pyrolytic liquids contain a high concentration of phenolic compounds because of a significant presence of lignins and other high molecular weight compounds in the original material. Moreover, the generated non-condensable gases consist mainly of short-chain compounds, such as alcohols, aldehydes, and alkenes produced from hemicellulose, cellulose, and proteins.

The impact of combined application of biochar and fertilizer on the biochemical properties of soil in soybean fields

Background

Heilongjiang Province is a major soybean production area in China. To improve soil structure and increase soybean yield, this study examined the effects of combined biochar and chemical fertilizer application on the biochemical properties of soil in a maize-soybean rotation system.

Methods

The research were conducted from 2021 to 2022 at Heshan Farm Science Park in Heilongjiang Province, this field plot experiment utilized two soybean varieties, Heihe 43 (a high-protein variety) and Keshan 1 (a high-oil variety). In 2021, two plots with similar fertility levels were selected for planting soybeans and maize. In 2022, a maize-soybean rotation was implemented with five treatments: conventional fertilization (CK), increased biochar+reduced fertilizer 1 (F1+B), reduced fertilizer 1 (F1), increased biochar+reduced fertilizer 2 (F2+B), and reduced fertilizer 2 (F2). The study systematically analyzed the effects of combined biochar and chemical fertilizer application on soil chemical properties and microbial characteristics.

Results

Over 2 years, results showed that combined application effectively improved soil chemical traits. Compared to conventional fertilization (CK) and reduced fertilization (F1, F2), t he combined application of biochar and chemical fertilizer (F1+B, F2+B) increased soil pH, EC and the absolute value of zeta potential of soil surface, the CEC of soil significantly increased by 15.6-44.3%, the soil surface charge density and the soil surface charge quantity significantly increased by 16.4-73.5%. The combined application of biochar and chemical fertilizer also effectively enhanced the abundance and diversity of soil microbes. Dominant bacterial groups in soybean field soils under different treatments included Actinobacteria, Acidobacteria, Chloroflexi, and Proteobacteria; while dominant fungal groups were Ascomycota, Basidiomycota, and Mortierellomycota. Alpha and Beta diversity analyses revealed that the F1+B treatment significantly enhanced the species richness and diversity of bacteria and fungi in the soil, increasing the proportion and evenness of dominant and beneficial genera.

Terra Preta production from Ghanaian and Zambian soils using domestic wastes

Quests for productive soils to close yield gaps call for innovative strategies. This study tested an off-site formation of the Amazonian Terra Preta (TP) in a potential modern analogon under coastal savannah climatic conditions of Ghana. Four Ghanaian and two Zambian soils; two types of biochar (i.e., rice husk biochar and charcoal residues); domestic wastes (i.e., kitchen leftovers, animal manures, human urine, and kitchen ash) were mixed with the soils wetted to 100% water holding capacity, and incubated under aerobic conditions for nine months. Indicators of the TP include total carbon (C), pH, base saturation, basic cations, and plant-available P, which were measured using standard methods of soil analysis. The TP formation enhanced soil pH by 0.02 to 2.9, ranging from pH 7.2 to 8.2, with charcoal residues having the highest effect on pH. The modern TP was characterized by relatively high total C, pH, K, Ca, Mg, Na, base saturation, and plant-available P. These properties reflect unique interactions between the chars, wastes, and soils, suggesting the potential for on-site TP formation. It calls for further studies, commitment, and perseverance in their formation in the future.

Facilitating Intracellular Electron Bifurcation by Mediating Flavin-Based Extracellular and Transmembrane Electron Transfer: A Novel Role of Pyrogenic Carbon in Dark Fermentation for Hydrogen Production

Pyrogenic carbon is considered an enhancer to H2-yielding dark fermentation (DF), but little is known about how it regulates extracellular electron transfer (EET) and influences transmembrane respiratory chains and intracellular metabolisms. This study addressed these knowledge gaps and demonstrated that wood waste pyrogenic carbon (biochar) could significantly improve the DF performance; e.g., addition of pyrogenic carbon produced by pyrolysis at 800 °C (PC800) increased H2 yield by 369.7%. Biochemical quantification, electrochemical analysis, and electron respiratory chain inhibition tests revealed that PC800 promoted the extracellular flavin-based electron transfer process and further activated the acceleration of the transmembrane electron transfer. Comparative metagenome/metatranscriptome analyses indicated that the flavin-containing Rnf complex was the potential transmembrane respiratory enzyme associated with PC800-mediated EET. Based on NADH/NAD+ circulation, the promoted Rnf complex could stimulate the functions of the electron bifurcating Etf/Bcd complex and startup of glycolysis. The promoted Etf/Bcd could further contribute to balance the NADH/NAD+ level for glycolytic reactions and meanwhile provide reduced ferredoxin for group A1 [FeFe]-hydrogenases. This proton-energy-linked mechanism could achieve coupling production of ATP and H2. This study verified the important roles of pyrogenic carbon in mediating EET and transmembrane/intracellular pathways and revealed the crucial roles of electron bifurcation in DF for hydrogen production.

Biochar and soil contributions to crop lodging and yield performance - A meta-analysis

Applying biochar has beneficial effects on regulating plant growth by providing water and nutrient availability for plants due to its physicochemical characteristics. Nevertheless, it is still unclear how soil and biochar interactions strengthen crop lodging resistance. The objective of the current study was to find out how soil physicochemical conditions and alterations in biochar affect lodging resistance and crop productivity in cereals. To do this, a meta-analysis was carried out using nine groups of effective variables including type of feedstock, pyrolysis temperature, application rate, soil pH, total nitrogen, available phosphorus, potassium, organic matter (OM), and soil texture. Results showed that straw-derived biochar caused the highest positive effect size in the dry weight of biomass (20.5%) and grain yield (19.9%). Also, the lowest lodging index was observed from straw (-8.3%) and wood-based (-5.6%) biochars. Besides, the high application rate of biochar results in the highest positive effect sizes of plant cellulose (8.1%) and lignin content (7.6%). Soils that contain >20 g kg-1 OM, resulted in the highest positive effect size in dry biomass (27.9%), grain yield (30.2%), and plant height (4.7%). Also, fine-textured soil plays an important role in increasing polymers in the anatomical structure of plants. Overall, the strong connection between biochar and soil processes, particularly the availability of OM, could strengthen plants' ability to tolerate lodging stress and contribute to high nutrient efficiency in terms of crop output and cell wall thickening.

Optimizing native vegetation establishment in urban soils: Assessing the impacts of organic amendments on specific growth parameters

Following soil disturbances, establishing healthy roadside vegetation can reduce surface water runoff, improve soil quality, decrease erosion, and enhance landscape aesthetics. This study explores the use of organic soil amendments (OAs) as alternatives to conventional vegetation growth approaches, aiming to provide optimal compost mixing ratios for poor soils, and clarify guidelines for OAs' use in roadside projects. Three sandy loam soils and one loam soil were chosen for the study. Organic amendments included yard waste (Y), food waste (F), turkey litter and green waste-based (T) composts, and wood-derived biochar (B). Treatment applications targeted specific increases in the organic matter (OM) percentage of the soils. A selection of seven native species (grasses and forbs) in a total of 156 pots (4 control soils + 4 soils x 4 OAs x 3 application rates, all prepared in triplicates) was used for the pot study experiment. A significant correlation between electrical conductivity (soluble salts) in soil-OA blends and corresponding percent green coverage (%GC) was found. High salts from the T compost either delayed or curtailed growth. Notably, 3 out of the 4 soils amended with biochar exhibited rapid vegetation coverage during initial growth stages compared to other soil-OA blends but reduced the nitrogen (N) uptake and leaf area in black-eyed Susan (BES) plants. In contrast, N uptake was higher in the BES plants emerging from composts T, F, and Y compared to biochar. It is recommended to minimize concentrated manure-based (e.g., turkey litter) composts for roadside projects as an OM source, and alternatively, enriching wood-based biochar with nutrients when used as a soil amendment. Within the current study, composts such as F and Y were well-suited to establish healthy and long-lasting vegetation.

Effects of the combination of biochar and organic fertilizer on soil properties and agronomic attributes of soybean (Glycine max L.)

This research aimed to investigate the impacts of a combination of rice husk biochar and organic fertilizer on the physical and chemical properties of soil, the population of soil bacteria, the relative chlorophyll content of leaves, the development of soybean root nodules, and yield components under strongly acid soil conditions. A greenhouse and pot experiment was designed using a randomize complete block design with factorial 2 × 3 treatments and three replications. The experimental treatments comprised two rates of biochar (35 and 70 g/pot) and three rates of organic fertilizer (70, 105, and 140 g/pot). After 100 days of amendment of strongly acidic soils, the results showed that application of treatments B35F70 and B70F140 increased soil pH by 16.80% compared to the control group (CK). On the other hand, treatments B35F140 and B70F105 resulted in an increase of soil electrical conductivity by 66.67% compared to CK. In addition, after 100 days of amendment with treatments B35F105, B35F105, B35F140, B70F105, B70F70, B70F70, and B35F140, organic matter, available phosphorous (P), potassium (K), calcium (Ca), magnesium (Mg), copper (Cu), and zinc (Zn), organic matter, available phosphorous (P), potassium (K), calcium (Ca), magnesium (Mg), copper (Cu), and zinc (Zn), significantly increased when compared to the control group (CK). Treatment B35F140 increased relative leaf chlorophyll content and soybean seed weight per plant by 60.76% and 100.56%, respectively when compared to the CK. Furthermore, treatment B35F70 produced 125% more root nodules than CK. Moreover, each amended strongly acid soil resulted with a significant upsurge in total soil bacteria compared to the CK. Overall, statistics proved that a combination of biochar and organic fertilizer improved soil properties and soybean agronomic attributes.

The Mechanism of Arsenic Release in Contaminated Paddy Soil with Added Biochar: The Role of Dissolved Organic Matter, Fe, and Bacteria

The addition of biochar inevitably modifies the acidity (pH), redox potential (Eh), and dissolved organic matter (DOM) level in the soil. These alterations also have coupled effects on the cycling of iron (Fe) and the composition of bacterial communities, thereby impacting the speciation and availability of arsenic (As) in the soil. This study explored the potential mechanisms through which biochar affects As in paddy soil during flooded cultivation with different pyrolysis temperature biochars (300 °C, 400 °C, and 500 °C) added. The results revealed that the TAs concentration increased in the initial 15 days of soil cultivation with SBC300 or SBC400 addition because increasing the concentration of DOM induced the mobility of As though the formation of As-DOM complexes. Meanwhile, biochar addition elevated the pH, decreased the Eh, and promoted the transformation of specific adsorbed As (A-As) and amorphous iron oxide-bound As (Amo-Fe-As) to supernatant As through enhancing the reductive dissolution of Fe(oxy)(hydr)oxides. Moreover, the biochar altered the relative abundance of As (V)-reducing bacteria (such as Firmicutes) and As (III)-oxidizing bacteria (such as Chloroflex), thereby affecting As speciation. However, these mechanistic effects varied depending on the pyrolysis temperature of the biochar. The microbial composition of SBC300 and SBC400 were similar, with both containing larger populations of Enterobacteriaceae (AsRB) and pseudomonas (FeRB) compared to CK and SBC500. It was proposed that lower pyrolysis temperatures (300 °C and 400 °C) are more favorable for the dissolution of Fe(oxy)(hydr)oxides and the reduction of As (V). However, the biochar from the higher pyrolysis temperature (500 °C) showed environmental impacts akin to the control group (CK). This study demonstrated potential mechanisms of biochar's effect on As and the role of pyrolysis temperature.

A comparison between constructed wetland substrates: Impacts on microbial community and wastewater treatment

Constructed wetlands (CWs) can play a crucial role in treating wastewater, and in the context of this study, the distillation byproduct of the whisky industry known as 'spent lees'. Here, we assess several different CW substrates (pea gravel, LECA and Alfagrog), with and without the addition of 20% biochar, in mesocosms set up to treat spent lees. Among the substrates tested, LECA + biochar and gravel + biochar showed promising results, with greater dissolved copper (dissCu) reduction, chemical oxygen demand (COD) removal, organic carbon (OC) reduction, and pH modulation. These findings indicate a potentially beneficial role for biochar in enhancing treatment efficacy, particularly in facilitating dissCu remediation and the removal of organic pollutants. In terms of microbial diversity, mesocosms including biochar generally had reduced bacterial alpha diversity, suggesting that 'fresh' (uncolonized) biochar may negatively affect microbial diversity in wetland ecosystems in the short term. After continuously supplying spent lees to mesocosms for 2-months, microbial diversity in each mesocosm dropped substantially, and moderate levels of bacterial community differentiation and high levels of fungal community differentiation were detected among mesocosms. The bacterial and fungal communities were also found to differ between the substrate and outlet water samples. Among the bacterial classes present in the mesocosms that may play a crucial role in water treatment performance, Gammaproteobacteria, Bacteroidia and Alphaproteobacteria should be further investigated. In terms of fungal classes, the role of Sordariomycetes should be explored in greater depth.

Study on the Effect of Magnesium Chloride-Modified Straw Waste Biochar on Acidic Soil Properties

Soil biochar is a kind of organic matter rich in carbon, which is of great significance in soil fertility improvement, fertilizer type innovation and greenhouse gas emission reduction. In this paper, Mg-modified biochar was prepared by thermal cracking using rice straw and corn straw as raw materials. The Mg-modified biochar and unmodified biochar were fully mixed with prepared soil samples at the addition amounts of 0.5% (w/w), 1% (w/w) and 2% (w/w), respectively, and then simulated indoor soil cultivation experiments were carried out. The effects of magnesium ion-modified biochar and non-modified biochar on soil chemical properties and the effects of different amounts of biochar on soil properties were studied. The results showed that the yield of Mg-modified biochar from rice straw and corn straw, prepared by pyrolysis, was 65%, and the ash content was large. The pH of MG-modified corn stalk biochar (MCBC) is weakly basic (8.55), while the pH of MG-modified rice stalk biochar (MRBC) is basic (10.1), and their internal structures are slightly different. After the application of biochar prepared from rice straw and maize stover, soil indicators were determined. Compared to the control, the chemical properties of the treated soil samples were significantly improved, with an increase in soil pH, an increase in the content of effective nutrients, such as fast-acting potassium, fast-acting phosphorus and alkaline dissolved nitrogen, and an increase in the content of the total phosphorus and total nitrogen, as well as an increase in the content of organic matter. The Mg-modified biochar was generally superior to the unmodified biochar in improving soil fertility, at the same addition level. It was also found that the rice-straw biochar performed better than the corn-stover biochar and had a more obvious effect on soil improvement in terms of fast-acting potassium, ammonium nitrogen, nitrate nitrogen, total phosphorus and total nitrogen contents.

Wood ash application for crop production, amelioration of soil acidity and contaminated environments

Agriculture is vital to human life and economic development even though it may have a detrimental influence on soil quality. Agricultural activities can deteriorate the soil quality, endangers the ecosystem health and functioning, food safety, and human health. To resolve the problem of soil degradation, alternative soil conditioners such as wood ash are being explored for their potential to improve soil-plant systems. This study provides an overview of the production, properties, and effects of wood ash on soil properties, crop productivity, and environmental remediation. A comprehensive search of relevant databases was conducted in order to locate and assess original research publications on the use of wood ash in agricultural and environmental management. According to the findings, wood ash, a byproduct of burning wood, may improve the structure, water-holding capacity, nutrient availability, and buffering capacity of soil as well as other physico-chemical, and biological attributes of soil. Wood ash has also been shown to increase agricultural crop yields and help with the remediation of polluted regions. Wood ash treatment, however, has been linked to several adverse effects, such as increased trace element concentrations and altered microbial activity. The examination found that wood ash could be a promising material to be used as soil conditioner and an alternative supply of nutrients for agricultural soils, while, wood ash contributes to soil improvement and environmental remediation, highlighting its potential as a sustainable solution for addressing soil degradation and promoting environmental sustainability in agricultural systems.

Gasification chars and activated carbon: Systematic physico-chemical characterization and effect on biogas production

Gasification residues/chars (GR) and activated carbon (AC) are added to wastewater treatment processes mainly as a fourth purification stage, e.g., to adsorb heavy metals or pharmaceutical residues. However, the effects of GR or AC, which are transferred to the anaerobic digestion (AD) via the sludge, are not yet fully understood. Although, the positive effect of char addition on AD has been demonstrated in several investigations, systematic studies with chemically well described chars are still missing. Therefore, in this study, different chars were characterized in detail, subjected to AD in different concentrations, and their effect on methane production investigated. GR of a gasification plant with a floating fixed bed technology, carbon made by chemical impregnation with ZnCl2 from waste-wood, carbon produced by thermochemical activation with CO2 from GR and commercial powdered AC were used for the experiments. Among others, thermogravimetric analysis, physisorption, pH, and conductivity analysis were used to characterize the chars. Mesophilic AD batch tests with different concentrations (0.025, 0.05, 0.5, 1.0, 7.0, 14.0 gL-1) of all chars (GR and ACs, respectively) were performed with digester sludge from a wastewater treatment plant for a period of 47 d. Volatile fatty acids (VFA) as well as biogas production and CH4 concentrations were monitored. It could be shown, that concentrations below 1.0 g char L-1 did not result in significant effects on CH4 and/or VFA production, whereas high concentrations of GR and AC influenced both, the CH4 yield and kinetics. Depending on the production process and the characteristics of the chars, the effect on AD varied, whereby both, positive and negative effects on biogas yield and methane production were observed. This study provides the first systematic evaluation of char application to AD processes, and therefore allows for better predictions of char applicability and effect.

Exploring the environmental pathways and challenges of fluoroquinolone antibiotics: A state-of-the-art review

Fluoroquinolone (FQ) antibiotics have become a subject of growing concern due to their increasing presence in the environment, particularly in the soil and groundwater. This review provides a comprehensive examination of the attributes, prevalence, ecotoxicity, and remediation approaches associated with FQs in environmental matrices. The paper discusses the physicochemical properties that influence the fate and transport of FQs in soil and groundwater, exploring the factors contributing to their prevalence in these environments. Furthermore, the ecotoxicological implications of FQ contamination in soil and aquatic ecosystems are reviewed, shedding light on the potential risks to environmental and human health. The latter part of the review is dedicated to an extensive analysis of remediation approaches, encompassing both in-situ and ex-situ methods employed to mitigate FQ contamination. The critical evaluation of these remediation strategies provides insights into their efficacy, limitations, and environmental implications. In this investigation, a correlation between FQ antibiotics and climate change is established, underlining its significance in addressing the Sustainable Development Goals (SDGs). The study further identifies and delineates multiple research gaps, proposing them as key areas for future investigational directions. Overall, this review aims to consolidate current knowledge on FQs in soil and groundwater, offering a valuable resource for researchers, policymakers, and practitioners engaged in environmental management and public health.

Recovery of biochar particles laden with lead in saturated porous media by DC electric field

The co-transport behavior of environmental pollutants with biochar particles has aroused great interests from researchers due to the concerns about pollutant diffusion and environmental exposure after biochar is applied to soil. In this work, the recovery and co-transport behavior of biochar micron-/nano-particles (BCMP and BCNP) and lead (Pb2+) in saturated porous media were investigated under different ionic strength conditions (IS = 1, 5 and 10 mM) under a direct current electric field. The results showed that the electric field could significantly enhance the mobility of Pb adsorbed biochar particles, particularly BCNP. The recovery of Pb laden biochar particles was improved by 1.8 folds, reaching 78.8% at maximum under favorable condition at +0.5 V cm-1. According to the CDE (Convection-Dispersion-Equation) model and DLVO (Derjaguin-Landau-Verwey-Overbeek) theory analysis, the electric field facilitated the transport of Pb carried biochar mainly by increasing the negative charges on biochar surface and improving the repulsive force between biochar and porous media. High IS was favorable for biochar transport under the electric field, but inhibited desorbing Pb2+ from biochar (18% by maximum at IS = 10 mM). By switching the electric field power, a two-stage strategy was established to maximize the recovery of both biochar particles and Pb, where BCNP and Pb recovery were higher than electric field free case by 90% and 35%, respectively. The findings of this study can help build a biochar recovery approach to prevent potential risks from biochar application in heavy metal contaminated soil remediation.

Feedstock and pyrolysis temperature influence biochar properties and its interactions with soil substances: Insights from a DFT calculation

The use of biochar for soil improvement and emission reduction has been widely recognized for its excellent performance. However, the choice of feedstock and pyrolysis temperature for biochar production significantly affects its surface parameters and interactions with soil substances. In this study, we retrieved 465 peer-reviewed papers on the application of biochar in reducing greenhouse gas emissions and nutrient losses in soil and analyzed the changes in biochar physicochemical parameters from different feedstock and pyrolytic temperatures. Molecular simulation computing technology was also used to explore the impacts of these changes on the interaction between biochar and soil substances. The statistical results from the peer-reviewed papers indicated that biochar derived from wood-based feedstock exhibits superior physical characteristics, such as increased porosity and specific surface area. Conversely, biochar derived from straw-based feedstock was found to contain excellent element content, such as O, N, and H, and biochar derived from straw and produced at low pyrolysis temperatures contains a significant number of functional groups that enhance the charge transfer potential and adsorption stability by increasing surface charge density, charge distribution and bonding orbitals. However, it should be noted that this enhancement may also activate certain recalcitrant C compounds and promote biochar decomposition. Taken together, these results have significant implications for biochar practitioners when selecting suitable feedstock and pyrolysis temperatures based on agricultural needs and increasing their understanding of the interaction mechanism between biochar and soil substances.

Removal and release of microplastics and other environmental pollutants during the start-up of bioretention filters treating stormwater

Untreated stormwater is a major source of microplastics, organic pollutants, metals, and nutrients in urban water courses. The aim of this study was to improve the knowledge about the start-up periods of bioretention filters. A rain garden pilot facility with 13 bioretention filters was constructed and stormwater from a highway and adjacent impervious surfaces was used for irrigation for ∼12 weeks. Selected plants (Armeria maritima, Hippophae rhamnoides, Juncus effusus, and Festuca rubra) was planted in ten filters. Stormwater percolated through the filters containing waste-to-energy bottom ash, biochar, or Sphagnum peat, mixed with sandy loam. Influent and effluent samples were taken to evaluate removal of the above-mentioned pollutants. All filters efficiently removed microplastics >10 µm, organic pollutants, and most metals. Copper leached from all filters initially but was significantly reduced in the biochar filters at the end of the period, while the other filters showed a declining trend. All filters leached nutrients initially, but concentrations decreased over time, and the biochar filters had efficiently reduced nitrogen after a few weeks. To conclude, all the filters effectively removed pollutants during the start-up period. Before being recommended for full-scale applications, the functionality of the filters after a longer period of operation should be evaluated.

Biochar obtained from eucalyptus, rice hull, and native bamboo as an alternative to decrease mobility of hexazinone, metribuzin, and quinclorac in a tropical soil

Mobile herbicides have a high potential for groundwater contamination. An alternative to decrease the mobility of herbicides is to apply materials with high sorbent capacity to the soil, such as biochars. The objective of this research was to evaluate the effect of eucalyptus, rice hull, and native bamboo biochar amendments on sorption and desorption of hexazinone, metribuzin, and quinclorac in a tropical soil. The sorption-desorption was evaluated using the batch equilibrium method at five concentrations of hexazinone, metribuzin, and quinclorac. Soil was amended with eucalyptus, rice hull, and native bamboo biochar at a rate of 0 (control-unamended) and 1% (w w-1), corresponding to 0 and 12 t ha-1, respectively. The amount of sorbed herbicides in the unamended soil followed the decreasing order: quinclorac (65.9%) > metribuzin (21.4%) > hexazinone (16.0%). Native bamboo biochar provided the highest sorption compared to rice hull and eucalyptus biochar-amended soils for the three herbicides. The amount of desorbed herbicides in the unamended soil followed the decreasing order: metribuzin (18.35%) > hexazinone (15.9%) > quinclorac (15.1%). Addition of native bamboo biochar provided the lowest desorption among the biochar amendments for the three herbicides. In conclusion, the biochars differently affect the sorption and desorption of hexazinone, metribuzin, and quinclorac mobile herbicides in a tropical soil. The addition of eucalyptus, rice hull, and native bamboo biochars is a good alternative to increase the sorption of hexazinone, metribuzin, and quinclorac, thus, reducing mobility and availability of these herbicides to nontarget organisms in soil.

Predictive modelling of methane yield in biochar-amended cheese whey and septage co-digestion: Exploring synergistic effects using Gompertz and neural networks

This study performed bench scale studies on anaerobic co-digestion of cheese whey and septage mixed with biochar (BC) as additive at various dosages (0.5 g, 1 g, 2 g and 4 g) and total solids (TS) concentrations (5%, 7.5%, 10%,12.5% and 15%). The experimental results revealed 29.58% increase in methane yield (486 ± 11.32 mL/gVS) with 27% reduction in lag phase time at 10% TS concentration and 50 g/L of BC loading. The mechanistic investigations revealed that BC improved process stability by virtue of its robust buffering capacity and mitigated ammonia inhibition. Statistical analysis indicates BC dosage had a more pronounced effect (P < 0.0001) compared to the impact of TS concentrations. Additionally, the results were modelled using Gompertz model (GM) and artificial neural network (ANN) algorithm, which revealed the outperformance of ANN over GM with MSE 17.96, R2 value 0.9942 and error 0.27%. These findings validated the practicality of utilizing a high dosage of BC in semi-solid anaerobic digestion conditions.

Application of coconut shell activated carbon filter in vertical subsurface flow constructed wetland for enhanced multi-metal bioremediation and antioxidant response of Salvinia cucullate

Coconut shell activated carbon (CNSAC) was applied as a filter layer in hybrid vertical subsurface flow constructed wetland (H-VSSF-CW), in order to enhance the multi-metal removal efficiency of the constructed wetland (CW) and to reduce heavy metal accumulation on Salvinia cucullata. Treatment P + AC, (having CNSAC filter layer), showed 32, 21 and 34% more Cd, Cr, and Pb removal efficiency than treatment P (without CNSAC layer). CNSAC activated carbon adsorbed Cd and Pb and Cr by functional groups -NH, -NO2, -C-O, -OH and -CO, and significantly reduced Cd and Pb exposure to S. cucullate. Chromium adsorption by CNSAC filter layer was half (just 25% of total input) of the Cd and Pb. In treatment P, due to high Cd, Pb and Cr accumulation in S. cucullate, the antioxidant defense mechanism of the plant was collapsed and cell death was observed, which in turn has resulted reduced biomass gain (5% reduction). On the other hand, in treatment P + AC, an antioxidant defense mechanism was active in the form significantly (p ≤ 0.05) increased of SOD, CAT and proline content while reduced MDA, EL, %EB and soluble sugar. So, the application of CNSAC increased the heavy metal removal efficiency of H-VSSF-CW by adsorption of a considerable share of heavy metal and hence, reduced the heavy metal load/exposure to S. cucullate.

Reducing nitrogen loss from farmland by layered double hydroxide-supported carbon dots-enhanced ammonium immobilization

It remains a significant challenge to develop a kind of cost-effective and eco-friendly adsorbent with strong immobilization capabilities for ammonium in farmland. In this work, we employed Ca/Al layered double hydroxide-supported carbon dots (CDs@Ca/Al-LDHs) as a novel and efficient adsorbent for ammonium immobilization both in aqueous and soil environments. Such a composite could exhibit a high adsorption capacity towards ammonium in solution, which was four times higher than zeolite and three times higher than biochar under the same conditions. The mechanism investigations revealed that electrostatic interactions between the negatively charged CDs and the positively charged ammonium played a key role in the adsorption. In 30-day leaching experiments, the fabricated composite cumulatively reduced ammonium and nitrate by 6.3% and 9.7%, respectively at a dosage of 0.1% (w/w). Incubation experiments further confirmed that the developed composite could effectively inhibit ammonia volatilization and nitrification by immobilizing the ammonium within soil matrices. Our results demonstrated that CDs@Ca/Al-LDHs represented a promising candidate for cost-effective and eco-friendly immobilization of excess ammonium from over-fertilized farmland.

Three-year field experiments revealed the immobilization effect of natural aging biochar on typical heavy metals (Pb, Cu, Cd)

Biochar has been widely used for the remediation of heavy metal contaminated soil, while the long-term field aging on its properties and the performance in the ability of metal immobilization must not be overlooked. In this study, the stability of immobilized heavy metals (Cd, Cu, Pb) on biochar during a 3-year remediation for soil in the field was investigated through desorption experiments. The results indicated that the application of biochar and its aging in the field both remarkably increased the immobilization of the 3 metal ions in the field under 3-year remediation. The cumulative desorption of the 3 metals decreased with biochar aging, and the desorption rate of Pb2+, Cu2+ and Cd2+ in T3 (Application of 30 t·hm-2 of biochar) for the third year was 0.08 %, 0.20 % and 13.15 %. Meanwhile, both the desorption rates and extents exhibited significant difference with the order of Pb2+ < Cu2+ < Cd2+. The increased soil pH, the enhancement of O/C ratio (Increase from 0.30 for fresh BC to 0.61 for aged BC(S3)) and oxygen-containing functional groups in biochar, and the accretion of organo-mineral micro-agglomerates on biochar surfaces and in pores during field aging process jointly contributed the immobilization of metals in soils mainly through co-precipitation and complexation. Our results provide new insights into the practical application of biochar in soils contaminated with multiple heavy metals from the perspective of long-term effects, which suggests that the potential release risk of metals become slighter over time.

Structural and functional perspectives of carbon filter media in constructed wetlands for pollutants abatement from wastewater

Constructed wetlands (CWs) represent the most viable artificial wastewater treatment system that works on the principles of natural wetlands. Filter media are integrally linked to CWs and have substantial impacts on their performance for pollutant removal. Carbon-derived substrates have been in the spotlight for decades due to their abundance, sustainability, reusability, and potential to treat complex contaminants. However, the efficiency and feasibility of carbon substrates have not been fully explored, and there are only a few studies that have rigorously analyzed their performance for wastewater treatment. This critical synthesis of the literature review offers comprehensive insights into the utilization of carbon-derived substrates in the context of pollutant removal, intending to enhance the efficiency and sustainability of CWs. It also compares several carbon-based substrates with non-carbon substrates with respect to physiochemical properties, pollutant removal efficiency, and cost-benefit analysis. Furthermore, it addresses the concerns and possible remedies about carbon filtration materials such as configuration, clogging minimization, modification, and reusability to improve the efficacy of substrates and CWs. Recommendations made to address these challenges include pretreatment of wastewater, use of a substrate with smaller pore size, incorporation of multiple filter media, the introduction of earthworms, and cultivation of plants. A current scientific scenario has been presented for identifying the research gaps to investigate the functional mechanisms of modified carbon substrates and their interaction with other CW components.

Straw-derived biochar for the removal of antibiotics from water: Adsorption and degradation mechanisms, recent advancements and challenges

Antibiotics, a kind of containments with the properties of widely distributed and difficult to degrade, has aroused extensive attention in the world. As a prevalent agricultural waste, straws can be utilized to prepare biochar (straw-derived biochar, SBC) to remove antibiotics from aquatic environment. To date, although a number of review papers have summarized and discussed research on biochar application in wastewater treatment and soil remediation, there are few reviews on SBC for antibiotic removal. Due to the limitations of poor adsorption and degradation performance of the pristine SBC, it is necessary to modify SBC to improve its applications for antibiotics removal. The maximum antibiotic removal capacity of modified SBC could reach 1346.55 mg/g. Moreover, the adsorption mechanisms between modified SBC and antibiotics mainly involve π-π interactions, electrostatic interactions, hydrophobic interactions, and charge dipole interactions. In addition, the modified SBC could completely degrade antibiotics within 6 min by activating oxidants, such as PS, PDS, H2O2, and O3. The mechanisms of antibiotic degradation by SBC activated oxidants mainly include free radicals (including SO4•-, •OH, and O2•-) and non-free radical pathway (such as, 1O2, electrons transfer, and surface-confined reaction). Although SBC and modified SBC have demonstrated excellent performance in removing antibiotics, they still face some challenges in practical applications, such as poor stability, high cost, and difficulties in recycling. Therefore, the further research directions and trends for the development of SBC and biochar-based materials should be taken into consideration.

Biochar-assisted degradation of oxytetracycline by Achromobacter denitrificans and underlying mechanisms

Contamination of the environment with large amounts of residual oxytetracycline (OTC) and the corresponding resistance genes poses a potential threat to natural ecosystems and human health. In this study, an effective OTC-degrading strain, identified as Achromobacter denitrificans OTC-F, was isolated from activated sludge. In the degradation experiment, the degradation rates of OTC in the degradation systems with and without biochar addition were 95.01-100% and 73.72-99.66%, respectively. Biochar promotes the biodegradation of OTC, particularly under extreme environmental conditions. Toxicity evaluation experiments showed that biochar reduced biotoxicity and increased the proportion of living cells by 17.36%. Additionally, biochar increased the activity of antioxidant enzymes by 34.1-91.0%. Metabolomic analysis revealed that biochar promoted the secretion of antioxidant substances such as glutathione and tetrahydrofolate, which effectively reduced oxidative stress induced by OTC. This study revealed the mechanism at the molecular level and provided new strategies for the bioremediation of OTC in the environment.

Effects of four amendments on cadmium and arsenic immobilization and their exposure risks from pakchoi consumption

Exposure to heavy metal(loid)s (HM) through contaminated food chains poses significant health risks to humans. While soil amendments are known to reduce HM bioavailability, their effects on bioaccessibility and health risks in soil-pakchoi-human systems remain unclear. To address this knowledge gap, we conducted a greenhouse pot experiment coupling soil immobilization with bioaccessibility-based health risk assessment for Cd and As exposure from pakchoi consumption. Four amendments (attapulgite, shell powder, nanoscale zero-valent iron, and biochar) were applied to soil, resulting in changes to soil characteristics (pH and organic matter), plant dry weight, and exchangeable fractions of As and Cd. Among the tested amendments, biochar exhibited the highest effectiveness in reducing the risk of Cd and As exposure from pakchoi consumption. The bioaccessibility-based health risk assessment revealed that the application of 5% biochar resulted in the lowest hazard index, significantly decreasing it from 1.36 to 0.33 in contaminated soil. Furthermore, the structural equation model demonstrated that pH played a critical role in influencing remediation efficiency, impacting the exposure of the human body to Cd and As. In conclusion, our study offers a new perspective on mitigating exposure risks of soil HM and promoting safe crop production. The results underscore the importance of considering bioaccessibility in health risk assessment and highlight the potential of biochar as a promising amendment for reducing Cd and As exposure from pakchoi consumption.

Catalytic pyrolysis of biomass using fly ash leachate to increase carbon monoxide production and improve biochar properties to accelerate anaerobic digestion

Biomass-derived biochar is attracting growing interest as an effective additive for anaerobic digestion (AD). To improve energy yield and digestion performance through an integrated process of biochar production and AD, biochar upgrading using biomass fly ash leachate as a sustainable metal catalyst was investigated. The results indicate that the bark soaked in the leachate improved the pyrolysis reactivity of biomass with CO2 and reduced the temperature at which the reaction rate reached its maximum from 943 °C to 801 °C. This resulted in a doubling of CO production during CO2-assisted pyrolysis at 800 °C. In addition, the combined use of fly ash leachate and CO2 in bark pyrolysis improved not only the porosity of the resulting biochar but also its wettability and liming potential. Moreover, biochar amended with fly ash leachate and CO2 significantly reduced the lag time in the anaerobic digestion of grease trap waste.

Enhancing dissolved inorganic phosphorous capture by gypsum-incorporated biochar: Synergic performance and mechanisms

Excess nutrients, such as phosphorus (P), in watersheds jeopardize water quality and trigger harmful algal blooms. Using phosphorus sorption material (PSM) to capture P from wastewater and agricultural runoff can help recover nutrients and prevent their water pollution. In this study, a novel designer biochar was generated by pyrolyzing woody biomass pretreated with a flue gas desulfurization gypsum. The removal of dissolved inorganic phosphorus (DIP) by the gypsum-incorporated designer biochar was more efficient than the gypsum, suggesting the pretreatment of biomass with the gypsum results in a synergic effect on enhancing DIP capture. The maximum P adsorption capacity of the designer biochar was more than 200 mg g-1 , which is one order of magnitude greater than that of the gypsum. This result clearly showed that the designer biochar is a better PSM to capture DIP from nutrient-contaminated water compared to the gypsum. Post-sorption characterization indicated that the sorption of DIP by the gypsum-incorporated biochar involves multiple mechanisms. The precipitation reactions of calcium (Ca) cations and P anions to form CaHPO4 and Ca3 (PO4 )2 precipitates on the highly alkaline surface of the designer biochar were identified as a main mechanism. By contrast, CaHPO4 ·2H2 O is the only precipitated product for DIP sorption by the gypsum. In addition, the initial solution pH and the coexisting bicarbonate had less effects on the DIP removal by the designer biochar in comparison with the gypsum, which further confirms that the former is an excellent PSM to capture DIP from a variety of aquatic media.

Mercury reduction by black carbon under dark conditions

An accurate depiction of mercury (Hg) reduction is important to predict Hg biogeochemistry in both aquatic and soil systems. Although the photoreduction of Hg is well documented, reduction in the dark is poorly known and is thus the focus of this work. Black carbon (BC), an important constituent of organic matter in environments, can reduce Hg2+ in dark and oxygen-deficient conditions. Fast removal of Hg2+ in BC/Hg2+ solution was observed, with 4.99-86.88 L mg-1h-1 of the reaction rate constant, which could be ascribed to the combined actions of adsorption and reduction. Meanwhile, slow Hg reduction was obtained, compared to Hg removal, with 0.06-2.16 L mg-1h-1 of the reaction rate constant. Thus, in the initial stage, Hg2+ removal was mainly triggered by adsorption, rather than reduction. Afterward, the adsorbed Hg2+ on black carbon was converted into Hg0. Dissolved black carbon and aromatic CH on particulate black carbon were dominant triggers of Hg reduction for black carbon. During Hg reduction, the intastable intermediate, formed in the complex between aromatic CH and Hg2+, behaved as persistent free radicals, which could be detected by in situ electron paramagnetic resonance. Subsequently, the intastable intermediate was mainly converted into CO on black carbon and Hg0. Corresponding results of the present study highlight the important role of black carbon in the Hg biogeochemical cycle.

Characteristics of dissolved organic matter composition in biochar: Effects of feedstocks and pyrolysis temperatures

Biochar has widely used in soil pollution remediation due to its advantages of high efficiency and environmental sustainability. Dissolved organic matter (DOM) released by biochar plays a non-negligible role in the migration and transformation of pollutants in environment, and its composition was regarded as main impact factor. In this study, 28 biochar were investigated to detect the effect of pyrolysis temperature and feedstock on DOM content and components. Results showed that the content of DOM released from biochar at low pyrolysis temperatures (300-400 ℃) was higher than that from high pyrolysis temperatures (500-600 ℃). In addition, the specific UV-Visible absorbance at 254 nm (SUVA254) results expressed that DOM from peanut shell biochar (PSBC), rice husk biochar (RHBC) and bamboo biochar (BBC) had higher humification at high temperatures. Moreover, one fulvic acid-like (C2) and two humic acid-like (C1, C3) substances were main fluorescent components of biochar-derived DOM identified by parallel factor analysis based on excitation emission matrices fluorescence spectroscopies (EEM-PARAFAC). With the increase of pyrolysis temperature, humic acid substances content gradually decreased. The correlation analysis results revealed that pyrolysis temperatures and O/C, H/C, DOM content, the biological index (BIX), humification index (HIX), C1% and C3% was negatively correlated (p < 0.001). Thus, the pyrolysis temperatures take important roles in composition of DOM released from biochar, and this research would provide a reference for the application of biochar in the environment.

Effect of Mg-Modified Waste Straw Biochar on the Chemical and Biological Properties of Acidic Soils

Biochar is important for soil improvement, fertilizer innovation, and greenhouse gas reduction. In this paper, Mg-modified biochar was prepared from rice and corn straw and mixed with soil at a 1% (w/w) addition in an indoor soil simulation experiment to study the effect of Mg-modified biochar on the chemical properties of acidic soil. The results showed that the addition of Mg-modified biochar reduced soil acidity and improved soil fertility. Compared with the control group, the Mg-modified biochar treatment significantly increased the concentrations of available potassium, available phosphorus, total phosphorus, organic carbon and exchangeable calcium and magnesium in the soil, and effectively increased the concentration of total nitrogen. Rice straw Mg-modified biochar treatment was more effective in increasing the soil-available potassium, available phosphorus, total phosphorus and exchangeable magnesium concentration, while corn straw Mg-modified biochar was more effective in increasing the soil organic carbon and exchangeable calcium concentration. In addition, the high pyrolysis temperature of Mg-modified biochar was more effective in promoting the soil-available potassium, available phosphorus and total nitrogen concentration, while the low pyrolysis temperature of Mg-modified biochar was more effective in promoting soil alkaline nitrogen, exchangeable calcium and magnesium.

Dissolved biochar fractions and solid biochar particles inhibit soil acidification induced by nitrification through different mechanisms

Biochar can inhibit soil acidification by decreasing the H⁺ input from nitrification and improving soil pH buffering capacity (pHBC). However, biochar is a complex material and the roles of its different components in inhibiting soil acidification induced by nitrification remain unclear. To address this knowledge gap, dissolved biochar fractions (DBC) and solid biochar particles (SBC) were separated and mixed thoroughly with an amended Ultisol. Following a urea addition, the soils were subjected to an incubation study. The results showed that both the DBC and SBC inhibited soil acidification by nitrification. The DBC inhibited soil acidification by decreasing the H⁺ input from nitrification, while SBC enhanced the soil pHBC. The DBC from peanut straw biochar (PBC) and rice straw biochar (RBC) decreased the H⁺ release by 16 % and 18 % at the end of incubation. The decrease in H⁺ release was attributed to the inhibition of soil nitrification and net mineralization caused by the toxicity of the phenols in DBC to soil bacteria. The abundance of ammonia-oxidizing bacteria (AOB) and total bacteria decreased by >60 % in the treatments with DBC. The opposite effects were observed in the treatments with SBC. Soil pHBC increased by 7 % and 19 % after the application of solid RBC and PBC particles, respectively. The abundance of carboxyl on the surface of SBC was mainly responsible for the increase in soil pHBC. Generally, the mixed application of DBC and SBC was more effective at inhibiting soil acidification than their individual applications. The negative impacts of dissolved biochar components on soil microorganisms need to be closely monitored.

Toxic effects of cadmium on the physiological and biochemical attributes of plants, and phytoremediation strategies: A review

Anthropogenic activities pose a more significant threat to the environment than natural phenomena by contaminating the environment with heavy metals. Cadmium (Cd), a highly poisonous heavy metal, has a protracted biological half-life and threatens food safety. Plant roots absorb Cd due to its high bioavailability through apoplastic and symplastic pathways and translocate it to shoots through the xylem with the help of transporters and then to the edible parts via the phloem. The uptake and accumulation of Cd in plants pose deleterious effects on plant physiological and biochemical processes, which alter the morphology of vegetative and reproductive parts. In vegetative parts, Cd stunts root and shoot growth, photosynthetic activities, stomatal conductance, and overall plant biomass. Plants' male reproductive parts are more prone to Cd toxicity than female reproductive parts, ultimately affecting their grain/fruit production and survival. To alleviate/avoid/tolerate Cd toxicity, plants activate several defense mechanisms, including enzymatic and non-enzymatic antioxidants, Cd-tolerant gene up-regulations, and phytohormonal secretion. Additionally, plants tolerate Cd through chelating and sequestering as part of the intracellular defensive mechanism with the help of phytochelatins and metallothionein proteins, which help mitigate the harmful effects of Cd. The knowledge on the impact of Cd on plant vegetative and reproductive parts and the plants' physiological and biochemical responses can help selection of the most effective Cd-mitigating/avoiding/tolerating strategy to manage Cd toxicity in plants.

The modified properties of sludge-based biochar with ferric sulfate and its effectiveness in promoting carbon release from particulate organic matter in rural household wastewater

The scarcity of carbon sources presents a significant challenge for the bio-treatment of rural domestic wastewater (RDW). This paper presented an innovative approach to address this issue by investigating the supplementary carbon source through in-situ degradation of particulate organic matter (POM) facilitated by ferric sulfate modified sludge-based biochar (SBC). To prepare SBC, five different contents of ferric sulfate (0%, 10%, 20%, 25%, and 33.3%) were added to sewage sludge. The results revealed that the pore and surface of SBC were enhanced, providing active sites and functional groups to accelerate the biodegradation of protein and polysaccharide. During the 8-day hydrolysis period, the concentration of soluble chemical oxidation demand (SCOD) increased and peaked (1087-1156 mg L^-1) on the fourth day. The C/N ratio increased from 3.50 (control) to 5.39 (25% ferric sulfate). POM was degraded the five dominant phyla, which were Actinobacteriota, Firmicutes, Synergistota, Proteobacteria, and Bacteroidetes. Although the relative abundance of dominant phyla changed, the metabolic pathway remained unchanged. The leachate of SBC (<20% ferric sulfate) was beneficial for microbes, but an excessive amount of ferric sulfate (33.3% ferric sulfate) could have inhibition effects on bacteria. In conclusion, ferric sulfate modified SBC holds the potential for the carbon degradation of POM in RDW, and further improvements should be made in future studies.

Permanganate activation by glucose-derived carbonaceous materials for highly efficient degradation of phenol and p-nitrophenol: Formation of hydroxyl radicals and multiple roles of carbonaceous materials

Owing to its inertness toward refractory organic pollutants and the release of Mn²⁺, the use of permanganate was limited in soil and groundwater remediation. The present study proposed an improvement strategy based on glucose-derived carbonaceous materials, which enhanced the potential of permanganate degrading organic pollutants. The glucose-derived carbonaceous material with 1000 °C charring temperature was named C1000, which was exploited in activating KMnO₄ for the elimination of refractory organic contaminants. The addition of C1000 in the KMnO₄ system triggered the degradation of refractory p-nitrophenol and quicken phenol degradation. Unlike the detection of Mn(III) species in a solo KMnO₄ system, the presence of C1000 facilitated the formation of ^•OH in the KMnO₄ system, which was confirmed by the use of quenchers such as methanol, benzoic acid, tertiary butanol, and carbonate. Additionally, the glucose-derived carbonaceous material played multiple roles in improving the performance of permanganate, including the enrichment of organic pollutants, donation of electrons to permanganate, and acting as an electron shuttle to facilitate the oxidation of organic pollutants by permanganate. The study's novel findings have the potential to expand the use of permanganate in the remediation of organic pollutants.

The Terra Preta Model soil for sustainable sedentary yam production in West Africa

Current declines in yam yields amidst increasing cultivated areas, land scarcity, and population surges call for more sustainable sedentary yam production systems. This study explored the nature of Amazonian Dark Earths (ADEs) as a basis for the formation of a related soil type known as the Terra Preta Model (TPM) soil for future sedentary yam systems. It builds on the influence of human beings in soil management and the formation of Anthrosols. Previous studies on the ADEs and biochar were synthesized to establish the fundamental assumptions required to form the TPM soil. The practical approach to forming the TPM soils is based on the intentional, integrated and prolonged use of biochar, municipal solid wastes, agro-industry wastes and products of ecological sanitation. Tillage options such as mounding, ridging, trenching and sack farming could be used for yam production on the TPM soils. Unlike natural soils, the longevity of ADE fertility is subject to debate depending on crops grown and cropping cycles. Therefore, a crop rotation plan is recommended to maintain the fertility of the TPM soils. The TPM soils, if adopted, are considered worthwhile for the long-term benefit of biodiversity conservation, efficient waste management, enhanced ecosystem services provided by soils and extensive adoption of ecological sanitation.

Pig manure biochar for contaminated soil management: nutrient release, toxic metal immobilization, and Chinese cabbage cultivation

Pig manure could be an effective fertilizer source for soil, but with high concentrations of xic elements. It has been shown that the pyrolysis method could largely reduce the environmental risk of pig manure. However, the comprehensive analysis of both toxic metals immobilization effect and environmental risk of pig manure biochar applied as a soil amendment is rarely addressed. To address the knowledge gap, this study was carried out with pig manure (PM) and pig manure biochar (PMB). The PM was pyrolyzed at 450 ℃ and 700 ℃, the corresponding biochar was abbreviated as PMB450 and PMB700, respectively. The PM and PMB were applied in a pot experiment growing Chinese cabbage (Brassica rape L. ssp. Pekinensis) with clay-loam paddy soil. The application rates of PM were set at 0.5% (S), 2% (L), 4% (M) and 6% (H). With the equivalent mass principle, PMB450 and PMB700 were applied at 0.23% (S), 0.92% (L), 1.84% (M), 2.76% (H), and 0.192% (S), 0.7% (L), 1.4% (M), 2.1% (H), respectively. Parameters of Chinese cabbage biomass and quality, total and available concentrations of toxic metals in soil, and soil chemical properties were systemically measured. The main results of this study showed that compared with PM, PMB700 was more effective than PMB450, which induced the highest reductions of Cu, Zn, Pb, and Cd contents in cabbage by 62.6%, 73.0%, 43.9%, and 74.3%, respectively. Both PM and PMB increased the total contents of metals (Cu, Zn, Pb, and Cd) in soil, and PMB decreased the mobility of Cu, Zn, Pb, and Cd at high application rates (≥2%). Treatment with H-PMB700 reduced CaCl₂ extractable Cu, Zn, Pb, and Cd by 70.0%, 71.6%, 23.3%, and 15.9%, respectively. For Cu, Zn, Pb, and Cd fractions with BCR extraction, PMB treatments, especially PMB700, were more effective than PM in decreasing the available fractions (F1 +F2 +F3) at high application rates (≥2%). Overall, pyrolysis with high temperature (e.g., 700 ℃) could significantly stabilize the toxic elements in PM and enhance PM's effect on toxic metals immobilization. The marked effects of PMB700 on toxic metal immobilization and cabbage quality improvement might be attributed to high ash contents and liming effect.

Characterization of selected dietary fibers microparticles and application of the optimized formulation as a fat replacer in hazelnut spreads

The present work demonstrates the application of the spray drying technique to produce microparticulates of different dietary fibers with particle sizes<10 µm. It examines their role as potential fat replacers for hazelnut spread creams. Optimization of a dietary fiber formulation containing inulin, glucomannan, psyllium husk, and chia mucilage to obtain high viscosity, water holding capacity, and oil holding capacity was conducted. Microparticles containing 46.1, 46.2, and 7.6 weight percentages of chia seed mucilage, konjac glucomannan, and psyllium husk showed a spraying yield of 83.45 %, a solubility of 84.63 %, and viscosity of 40.49 Pas. When applied to hazelnut spread creams, microparticles substituted palm oil by 100 %; they produced a product with a total unsaturated and saturated fat reduction of 41 and 77 %, respectively. An increase in dietary fibers of 4 % and a decrease in total calories of 80 % were also induced when compared with the original formulation. Hazelnut spread with dietary fiber microparticles were preferred by 73.13 % of the panelist in the sensory study due to an enhancement in brightness. The demonstrated technique could be used to increase the fiber content while decreasing the fat content in some commercial products, such as peanut butter or chocolate cream.

Nitrogen removal mechanisms in biochar-amended sand filters treating onsite wastewater

The performance of biochar-amended sand filters treating septic tank effluent (STE) was investigated in bench-scale columns. Softwood biochar showed higher NH₄ ⁺ -N adsorption capacity (1.3 mg N g^-1 ), and its water holding capacity (0.57 g ml^-1 ) was significantly higher than sand (0.26 g ml^-1 ). Two biochar amendment ratios (10% and 30%) were selected for STE treatment in short-term (20 days) and long-term (8 months) studies. During the short-term experiment, the overall total nitrogen removal efficiency was greater in biochar-amended sand columns (94.7%-95.6%) than in 100% sand columns (71.2%) due to the additional NH₄ ⁺ -N adsorption by biochar. Greater nitrification performance was also observed in biochar-amended columns (87.1%-96.3%) than in 100% sand columns (61.4%) during long-term operation when alkalinity was insufficient. The nitrification performance in biochar-amended columns resumed more quickly (<7 days) after sufficient alkalinity was amended. The density of total biomass and nitrifying bacteria in biochar-amended columns (30%) were significantly higher at all experimental stages, suggesting biochar served as a growth media for enhanced biomass growth. The alkalinity changes and STE composition fluctuation had little impact on the nitrification performance of the 30% biochar-amended sand columns. In addition, biochar surface functional groups and zeta potential changed little after long-term STE filtration. Collectively, the results demonstrated proper biochar amendment ratio (30%) could enhance the nitrification performance of sand filters treating STE by increasing the system hydraulic retention time, providing additional alkalinity for nitrification, and serving as a growth media for enhanced biomass growth.

Soil pH restricts the ability of biochar to passivate cadmium: A meta-analysis

Soil acidification is the main cause for aggravation of soil cadmium (Cd) pollution. Biochar treatment can increase the soil pH and decrease the Cd availability in soils. However, there is limited information in literature on the comprehensive assessment of the response of Cd fractions to biochar. Therefore, in the present meta-analysis study, we evaluate the response of Cd fractions to biochar application in soils with different pH and to further examine the effect of physicochemical properties of biochar on Cd. Results from the overall analysis indicated that biochar treatment increased the soil pH by 7.0%, thereby decreasing the amount of available Cd (37.3%). In acidic soil, biochar significantly reduced the acid-soluble fraction (Acid-Cd) of Cd by 36.8%, while Oxidizable fraction of Cd (Oxid-Cd, 20.9%) and Residual fraction of Cd (Resid-Cd, 22.2%) were significantly increased. In neutral soils, only Acid-Cd was significantly reduced (33.0%) in the presence of biochar. In alkaline soils, biochar caused significant reduction in Acid-Cd of 12.4% and an increase in Oxid-Cd and Resid-Cd of 26.6% and 47.8%, respectively. Further, our findings showed that biochar with cation exchange capacity >100 cmol⁺/kg effectively decreased Acid-Cd (32.4%), while biochar with the percentage of hydrogen <2% was more contributory in increasing Resid-Cd (64.3%). These results demonstrate the importance of soil pH in regulating the biological effectiveness of Cd in soil and the complexation between the functional groups of biochar and Cd, and provide key information for the remediation of Cd pollution in soils with different pH by biochar.

Enhanced biodegradation of thiamethoxam with a novel polyvinyl alcohol (PVA)/sodium alginate (SA)/biochar immobilized Chryseobacterium sp H5

Long-term and extensive usage of thiamethoxam, the second-generation neonicotinoid insecticide, has caused a serious threat to non-target organisms and ecological security. Efficient immobilized microorganism techniques are a sustainable solution for bioremediation of thiamethoxam contamination. A Gram-negative aerobic bacterium Chryseobacterium sp H5 with high thiamethoxam-degrading efficiencies was isolated from activated sludge. Then we developed a novel polyvinyl alcohol (PVA)/sodium alginate (SA)/biochar bead with this functional microbe immobilization to enhance the biodegradation and removal of thiamethoxam. Results indicated that the total removal and biodegradation rate of thiamethoxam with PVA/SA/biochar (0.7 %) beads with Chryseobacterium sp H5 immobilization at 30 °C and pH of 7.0 within 7 d reached about 90.47 % and 68.03 %, respectively, much higher than that using PVA/SA immobilized microbes (75.06 %, 56.05 %) and free microbes (61.72 %). Moreover, the PVA/SA/biochar (0.7 %) immobilized microbes showed increased tolerance to extreme conditions. Biodegradation metabolites of thiamethoxam were identified and two intermediates were first reported. Based on the identified biodegradation intermediates, cleavage of C-N between the 2-chlorothiazole ring and oxadiazine, dichlorination, nitrate reduction and condensation reaction would be the major biodegradation routes of thiamethoxam. Results of this work suggested the novel PVA/SA/biochar beads with Chryseobacterium sp H5 immobilization would be helpful for the effective bioremediation of thiamethoxam contamination.

Remediation of Pb-contaminated soil using biochar-based slow-release P fertilizer and biomonitoring employing bioindicators

Soil contamination by Pb can result from different anthropogenic sources such as lead-based paints, gasoline, pesticides, coal burning, mining, among others. This work aimed to evaluate the potential of P-loaded biochar (Biochar-based slow-release P fertilizer) to remediate a Pb-contaminated soil. In addition, we aim to propose a biomonitoring alternative after soil remediation. First, rice husk-derived biochar was obtained at different temperatures (450, 500, 550, and 600 °C) (raw biochars). Then, part of the resulting material was activated. Later, the raw biochars and activated biochars were immersed in a saturated KH₂PO₄ solution to produce P-loaded biochars. The ability of materials to immobilize Pb and increase the bioavailability of P in the soil was evaluated by an incubation test. The materials were incorporated into doses of 0.5, 1.0, and 2.0%. After 45 days, soil samples were taken to biomonitor the remediation process using two bioindicators: a phytotoxicity test and enzyme soil activity. Activated P-loaded biochar produced at 500 °C has been found to present the best conditions for soil Pb remediation. This material significantly reduced the bioavailability of Pb and increased the bioavailability of P. The phytotoxicity test and the soil enzymatic activity were significantly correlated with the decrease in bioavailable Pb but not with the increase in bioavailable P. Biomonitoring using the phytotoxicity test is a promising alternative for the evaluation of soils after remediation processes.